Change badger version in manifest version FAQ (#1074)
Change badger version in manifest version FAQ (#1074)

The badger version mentioned in manifest version mismatch FAQ has an
unsupported backup format. This commit changes the badger version in FAQ
from v1.5.5 to v1.6.0. v1.6.0 has the new backup format.
The backup format was changed in
https://github.com/dgraph-io/badger/commit/4e5cbcc8574b8258c0146d4d01539b6d48212f4a
commit.
dgraph-io/badger,dgraph-io/badger